1. Field of the Invention
This invention generally relates to leak detection devices and, more particularly, to a device useful for detecting low/trace concentration fluid components leaking from a fluid storage vessel, and to a fluid storage vessel assembly comprising such leak detection device. The leak detection device of the invention has utility, inter alia, as an environmental monitor for detection of hazardous gases during transport, storage and use of fluid storage vessels containing such gases.
2. Description of the Related Art
In the field of environmental gas monitoring, various means have been employed and/or proposed for the detection of low or trace concentrations of impurities, e.g., hazardous gas species, in air or other ambient gases.
The systems currently commercially available, such as the so-called MDA monitors or Kitagawa tubes, have basic design and operational deficiencies that limit their use. They are either costly, require significant maintenance (involving replacement of consumable elements, e.g., the frequent change of color tapes in MDA monitors), require frequent recalibration, or in some instances do not to measure the impurity species properly or provide useful readouts. The MDA monitor is sensitive only down to concentration levels on the order of about 5 ppm, and readings below that level are inaccurate.
These conventional types of environmental monitoring systems are fundamentally inapplicable to fluid storage vessels.
Thousands of fluid storage vessels, such as conventional gas cylinders, are handled, transported, and used to dispense fluids daily. Many of such fluid storage vessels contain toxic chemicals that are injurious to health and/or the environment if inadvertently or accidentally leaked to the ambient surroundings. There is, however, no known leak detection device designed for use with such fluid storage vessels.
The high cost and significant maintenance of MDA monitors and Kitagawa tubes render them cost-prohibitive for use with conventional gas cylinders. MDA monitors and Kitagawa tubes are also not physically robust, and thus are susceptible to being readily damaged even if they were otherwise fundamentally modifiable for use with conventional fluid storage vessels. The high maintenance required of MDA monitors and Kitagawa tubes, furthermore, renders these monitoring systems inapplicable to the highly mobile infrastructure and orientation of the gas cylinder industry.
In current practice, gas sampling devices (termed "sniffers") are typically used to sample the air or ambient gas in a railroad car, transshipment container, truck bed container, gas cabinet or other enclosure in which the gas cylinder is transported or stored, before the cylinder is placed into use. The sampled gas then is subjected to gas analysis for determination of the potential presence of hazardous gas species. This is time-consuming, requires significant effort and resources, and is inefficient.
There is, accordingly, a significant need in the art for a leak detection device which is accurate and reliable, which is easily fabricated and operated, and which is cost-effective, for use with fluid storage vessels such as gas storage cylinders.
Relative to the aspect of the invention hereinafter described and claimed, wherein the leak detection device of the invention comprises a piezoelectric crystal detector, relevant art includes the following:
U.S. Reissue Patent 35,544 to J. T. Snow (piezoelectric material having moisture-reactive metal oxide coating for detection of moisture in gas stream); PA1 U.S. Pat. No. 5,339,675 to Anthony J. DiLeo, et al. (piezoelectric material having a metal and/or metal hydride coating, for detection of oxygen and/or water in a gas stream); PA1 U.S. Pat. No. 5,661,226 to W. D. Bowers, et al. (surface acoustic wave monitor for detecting non-volatile residue contamination of an environment); PA1 U.S. Pat. No. 5,411,709 to Makoto Furuki, et al. (fluorescent/phosphorescent gas-sensitive film on piezoelectric element, irradiated to generate light output indicative of gas concentration); PA1 U.S. Pat. No. 5,061,140 to G. G. Neuburger (reactive gas detection system including array of quartz microbalance detectors coated with layer of zinc or zinc compound reactive with halogen gases); PA1 U.S. Pat. No. 5,056,355 to M. J. Hepher (piezoelectric crystal sensor for monitoring dust or particulates in gas stream); PA1 U.S. Pat. No. 4,730,478 to Andras Gedeon (gas component sensor including piezoelectric crystal with a surface layer of material for reversibly adsorbing the gas component); PA1 U.S. Pat. No. 4,637,987 to Karl Minten, et al. (gas sensor including piezoelectric element coated with film of manganese tertiary phosphine polymer complex for absorbing gas); PA1 U.S. Pat. No. 4,399,686 to A. R. Kindlund, et al. (piezoelectric crystal coated with silicone oil, preferably a silicone oil comprising a silicone glycol copolymer, for adsorption and sensing of halogenated hydrocarbons, e.g., anaesthetic gases such as halothane, enfluorane, metoxyfluorane and isofluorane); and PA1 U.S. Pat. No. 4,163,384 to C. B. Blakemore (moisture analyzer for measuring moisture in acid gas stream, including a piezoelectric crystal coated with polystyrene sulfonic acid or salt thereof, in which the coating has been stabilized by exposure to acid gas). PA1 a sensor element having a monitorable characteristic that changes in exposure to the content of the vessel; and PA1 a self-contained monitoring unit operatively coupled to the sensor element and arranged to respond to a change in the monitorable characteristic of the sensor element, by responsively producing an output indicative of the change in the monitorable characteristic. PA1 a fluid vessel; and PA1 a leak detection device secured in detection proximity to the vessel, said leak detection device comprising: